Influence of the pressure wire on the fractional flow reserve calculation: CFD analysis of an ideal vessel and clinical patients with stenosis.

BACKGROUND AND OBJECTIVE: Fractional Flow Reserve (FFR) is generally considered the gold standard in hemodynamics to assess the impact of a stenosis on the blood flow. The standard procedure to measure involves the displacement of a pressure guide along the circulatory system until it is placed next to the lesion to be analyzed. The main objective of the present study is to analyze the influence of the pressure guide on the invasive FFR measurements and its implications in clinical practice. METHODS: We studied the influence of pressure wires on the measurement of Fractional Flow Reserve (FFR) through a combination of Computational Fluid Dynamics (CFD) simulations using 45 clinical patient data with 58 lesions and ideal geometries. The analysis is conducted considering patients that were subjected to a computer tomography and also have direct measurements using a pressure guide. Influence of the stenosis severity, degree of occlusion and blood viscosity has also been studied. RESULTS: The influence of pressure wires specifically affects severe stenosis with a lumen diameter reduction of 50 % or greater. This type of stenosis leads to reduced hyperemic flow and increased coronary pressure drop. Thus, we identified that the placement of wires during FFR measurements results in partial obstruction of the coronary artery lumen, leading to increased pressure drop and subsequent reduction in blood flow. The severity of low FFR values associated with severe stenosis may be prone to overestimation when compared to stenosis without severe narrowing. These results have practical implications, particularly in the interpretation of lesions falling within the "gray zone" (0,75-0,80). CONCLUSIONS: The pressure wire's presence significantly alters the flow on severe lesions, which has an impact on the FFR calculation. In contrast, the impact of the pressure wire appears to be reduced when the FFR is larger than 0.8. The findings provide critical information for physicians, emphasizing the need for cautious interpretation of FFR values, particularly in severe stenosis. It also offers insights into improving the correlation between FFRct models and invasive measurements by incorporating the influence of pressure wires.

Impact of Enhanced Phagocytosis of Glycated Erythrocytes on Human Endothelial Cell Functions.

Diabetes is associated with a high mortality rate due to vascular complications. Chronic hyperglycemia in diabetes leads to enhanced oxidative stress and glycation. Here, we explored the impact of glycation on human erythrocyte characteristics and capacity to affect endothelial cell function following erythrophagocytosis. Native and glucose-mediated glycated erythrocytes were prepared and characterized in terms of structural and deformability modifications. Erythrocyte preparations were tested for their binding and phagocytosis capacity as well as the potential functional consequences on human endothelial cell lines and primary cultures. Oxidative modifications were found to be enhanced in glycated erythrocytes after determination of their deformability, advanced glycation end-product content and eryptosis. Erythrophagocytosis by endothelial cells was significantly increased when incubated in the presence of glycated erythrocytes. In addition, higher iron accumulation, oxidative stress and impaired endothelial cell permeability were evidenced in cells previously incubated with glycated erythrocytes. When cultured under flow conditions, cellular integrity was disrupted by glycated erythrocytes at microvessel bifurcations, areas particularly prone to vascular complications. This study provides important new data on the impact of glycation on the structure of erythrocytes and their ability to alter endothelial cell function. Increased erythrophagocytosis may have a deleterious impact on endothelial cell function with adverse consequences on diabetic vascular complications.

Haemodynamic-dependent arrest of circulating tumour cells at large blood vessel bifurcations as new model for metastasis.

Homing of circulating tumour cells (CTC) at distant sites represents a critical event in metastasis dissemination. In addition to physical entrapment, probably responsible of the majority of the homing events, the vascular system provides with geometrical factors that govern the flow biomechanics and impact on the fate of the CTC. Here we mathematically explored the distribution of velocities and the corresponding streamlines at the bifurcations of large blood vessel and characterized an area of low-velocity at the carina of bifurcation that favours the residence of CTC. In addition to this fluid physics effect, the adhesive capabilities of the CTC provide with a biological competitive advantage resulting in a marginal but systematic arrest as evidenced by dynamic in vitro recirculation in Y-microchannels and by perfusion in in vivo mice models. Our results also demonstrate that viscosity, as a main determinant of the Reynolds number that define flow biomechanics, may be modulated to limit or impair CTC accumulation at the bifurcation of blood vessels, in agreement with the apparent positive effect observed in the clinical setting by anticoagulants in advanced oncology disease.

Determination of hemodynamic risk for vascular disease in planar artery bifurcations.

Understanding hemodynamics in blood circulation is crucial in order to unveil the mechanisms underlying the formation of stenosis and atherosclerosis. In fact, there are experimental evidences pointing out to the existence of some given vessel configurations that are more likely to develop the above mentioned pathologies. Along this manuscript, we performed an exhaustive investigation in a simplified model aiming to characterize by means of physical quantities those regions and configurations in vessel bifurcations that are more likely to develop such pathologies. The two-fold analysis is based, on the one hand, on numerical simulations (via CFD) and, on the other hand, on experiments realized in an ad-hoc designed polydimethylsiloxane (PDMS) channel with the appropriate parameters and appropriate fluid flows. The results obtained demonstrate that low velocity regions and low shear stress zones are located in the outer walls of bifurcations. In fact, we found that there is a critical range of bifurcation angles that is more likely to vascular disease than the others in correspondence with some experimental evidence. The effect of the inflow velocity on this critical range is also analyzed.